Abstract Poor oral feeding with subsequent growth failure is an enormous problem for infants with complex congenital heart disease (CCHD) because persistent growth failure is associated with higher mortality following cardiac surgery, more post-operative complications, and delayed neurodevelopment. More than a quarter of all infants with CCHD and at least half of those with single ventricle disease have a feeding disorder by age 2 years, yet a thorough understanding of the specific issues with feeding in these infants is lacking. Clinical management for feeding often differs between infants with single ventricle disease and infants with biventricular disease, and both groups have feeding issues. However, differences in specific feeding behaviors and developmental skills between these two groups have not been described. Feeding is a dynamic process affected by multiple factors, conceptualized in dynamic systems theory as constraints that are defined as boundaries or limits on the ability to coordinate a task. Feeding constraints could be supportive (e.g., prescribed protocols) or limiting (e.g., severity of infant disease). The overall long-term goal of this research is to develop interventions to support and enhance oral feeding in infants with CCHD. The specific aims of the proposed project are to (1) characterize oral feeding dynamics during the initial hospitalization in newborn infants undergoing operative intervention for CCHD in the first month of life, (2) compare oral feeding dynamics and feeding constraints between infants with single ventricle versus biventricular disease, and (3) identify the relationships among feeding constraints, oral feeding dynamics, and feeding-related outcomes. Oral feeding dynamics (readiness to feed, behavioral and physiologic response) will be measured using the Early Feeding Skills (EFS) assessment tool for an overall assessment and the dynamic-EFS for a second-by-second analysis of videotaped feedings for relationships between behavior and physiologic response. Physiologic response will include continuous measures of heart rate, respiratory rate, oxygen saturation, and heart rate variability. Task constraints will be measured by type of milk consumed (breast milk or formula). All infants will be bottle fed, which is standard for these newborns with CCHD, and rate of milk flow will be controlled with exclusive use of Dr. Brown?s Preemie nipple. External constraints will be measured with unit feeding guidelines and prescribed feeding protocols. Internal constraints will be measured by infant severity of disease and age at surgery. Outcomes will be measured for individual feedings using measures of feeding performance including total intake, proficiency (percentage of prescribed intake), efficiency (rate of milk intake), and feeding duration. Outcomes at discharge will include feeding milestones, growth, use of occupational therapy services, tube feeding at discharge, and length of stay. Knowledge of the unique characteristics of feeding in this population will inform and enable development of interventions tailored to specific capacities for feeding, thus promoting the health and well-being of these vulnerable infants through reducing morbidity and mortality and enhancing neurodevelopment.